Millions of people in the United States suffer from neurological diseases such as Alzheimer's disease, stroke, and brain cancer. Advances in protein/gene profiling techniques and high throughput drug screening technologies have spawned many new drug candidates. However, the blood-brain barrier (BBB) will hamper the development and clinical realization of this new generation of neurotherapeutics. This is because unless a drug is small (<500 Da) and lipophilic, it does not effectively transport from the bloodstream, across the BBB, and into the brain. As a consequence of these restrictions on brain drug attributes, the uptake of most small molecule therapeutics is extremely limited, while protein and gene medicines are not BBB permeable. A noninvasive delivery method with considerable promise involves the employ of endogenous BBB transport mechanisms as a means to shuttle drug cargo from the blood to the brain. Such receptor-mediated transport systems can be targeted using the exquisite specificity of antibodies that are in turn linked to a drug payload that can include small molecules, proteins, or DNA therapeutics. After binding to the receptor on the blood side, the antibody-drug conjugate acts as an artificial substrate for the transporter and will transcytose across the BBB into the brain. Current approaches have yielded limited brain uptake because the targeted transporters are ubiquitously expressed, and the antibody targeting reagents have a lower than expected BBB permeability. Therefore, this proposal is focused on the discovery and characterization of novel antibody delivery vectors having improved brain specificity and transport efficiency. Large human single- chain antibody (scFv) libraries will be searched for novel antibodies that bind to and endocytose into brain endothelial cells via cognate cell surface transport systems. These antibodies will be tested for their ability to transcytose across an in vitro BBB model, and will be quantitatively ranked for transport efficiency based their BBB permeability. Finally, the brain targeting and transcytosing scFv will be grafted onto a human IgG scaffold for in vivo testing. Pharmacokinetic profiling will be performed to determine organ uptake of brain targeting IgG in the rat. Those antibodies exhibiting significant and specific brain uptake will have excellent potential as noninvasive brain drug delivery vectors. HEALTH RELEVANCE Identification of novel noninvasive routes for drug delivery to the brain would have a significant impact on our ability to translate new therapeutics into clinically viable drugs for the treatment of millions of patients who suffer from debilitating neurological diseases. In particular, delivery approaches coupling antibodies with BBB-specific transport systems would be no more invasive than an intravenous injection and allow delivery of a variety of drug cargoes including small molecules, genes, and proteins. [unreadable] [unreadable] [unreadable]